1. Field of the Invention
This invention relates to a method of film-coating hard capsule. In particular, the invention relates to a method of film coating for the production of enteric hard capsule preparations.
2. Description of the Prior Art
When orally administered, pharmaceutical preparations are generally disintegrated and absorbed in the stomach. When enterically coated, however, they are not disintegrated in the stomach but are transported to the intestine, where they are disintegrated, followed by absorption of the active ingredient and production of biological or pharmacological effects thereof. In cases where an active ingredient is decomposed or denatured under acidic conditions in the stomach and as a result loses its effects or where it produces some or other adverse effect, such as gastric mucosa irritation, the troubles in question can be obviated by providing the preparations with an enteric coating. The technique of enteric coating can also be applied to the production controlled release preparations.
The enteric preparations so far frequently used generally occur as granules, tablets, and capsules filled with enteric granules. However, some drugs are not suited for tablet production by compression molding but must be made up into enteric granules or capsules filled therewith. In such case, it is required that the granules should be uniform in shape and size and so forth so that they can have satisfactory enteric and acid-resistant characteristics. To meet such requirement, much skill and a large quantity of an enteric coating material are needed. Troublesomely, varied coating conditions are to be used according to drugs differing in granule shape and size.
Accordingly, an attempt has been made to provide drug-filled hard capsules with an enteric coating to give enteric capsules (cf. Japanese Patent Publication No. 22835/69). However, since the adhesion between coating materials and hard capsules is not good, undercoating with PVP (polyvinylpyrrolidone) is necessary in using conventional enteric coating techniques. In addition, conventional coating techniques are disadvantageous in that the cap-body joint portion of capsules is incompletely coated. If enteric capsules have an incompletely coated area, disintegration would start at that area already in the gastric juice and, as a result, the original object of enteric capsules could not be attained any more.